Programmable non-volatile memories (NVM) are useful in many applications because they retain stored information even when power is removed from the memory. There are many different types of programmable non-volatile memory including, but not limited to, programmable read only memory (PROM), electrically erasable ROM (EEPROM) and Flash memory. These memory types have several methods of charge storage including but not limited to placing charge on a Floating Gate or Silicon-Oxide-Nitride-Oxide-Silicon (SONOS) storage material or node.
Like other types of memory, programmable NVMs are usually constructed as an array of bit cells arranged in rows and columns. For programmable NVMs, high voltage signals are used to erase and write data to the memory cells of the non-volatile memory. These high voltage signals include voltages which are outside of a normal power supply range of the integrated circuit. For example, a high voltage signal for newer devices includes high voltage levels VPOS and VNEG (e.g., +4.7V and −3.6V), which are applied to SONOS devices for program and erase modes. The high voltage signals applied to the SONOS device is the sum of VPOS and VNEG, and thus, the voltage bias may reach up to 8.3V across the terminals.
As the interest for smaller and faster devices has increased, interest in SONOS device scale down has increased as well. However, the aforementioned high voltage signals used on devices with thicker gate oxides may cause stresses on the devices with thinner gate oxides. Although additional devices can be employed to mitigate such stresses, inclusion of such devices may increase costs and complicate circuit fabrication.